Place the mushrooms in a medium bowl. In a small bowl, whisk together the vinegar, oil, soy sauce, garlic, and black pepper. Pour over the mushrooms, then with your hands, toss to coat the mushrooms evenly with the liquid.: As the mushrooms go into the bowl you should notice a dry, earthy aroma, and they will feel cool to the touch. This step organizes the mushrooms for even coating, which matters because an even coating ensures uniform browning. A common mistake here is crowding the bowl with other items, which makes tossing awkward and uneven.
Transfer the mushrooms to your air fryer basket. Air fry at 375°F, shaking a few times throughout, until the mushrooms are browned to your liking, about 10 minutes. Transfer to a plate and immediately season with a pinch of salt. Sprinkle with herbs if desired.: The mixture should smell bright from the balsamic vinegar and fragrant from the garlic powder . Whisking emulsifies the oil into the vinegar and soy, which helps the liquid cling to the mushroom surfaces so they caramelize rather than steam. If you skip whisking, the oil may separate and the coating will be inconsistent.
Pour over the mushrooms, then with your hands, toss to coat the mushrooms evenly with the liquid: When you toss, notice the glossy sheen developing on the mushroom caps, and the liquid should be absorbed into the crevices. Using your hands feels more tactile than a spoon, letting you gauge how evenly each slice is coated. Avoid over-tossing which can bruise delicate pieces and cause water to release prematurely.
Transfer the mushrooms to your air fryer basket: Spread them in a single layer so hot air can circulate around each piece; you should be able to see individual caps rather than a mound. Proper spacing is crucial because overcrowding causes steaming instead of crisping. If you crowd the basket, pause and cook in batches to achieve the best texture.
Air fry at 375°F, shaking a few times throughout, until the mushrooms are browned to your liking, about 10 minutes: As they cook the kitchen will fill with an intense roasted, slightly sweet aroma from the balsamic vinegar and caramelized mushroom sugars. Listen for a faint sizzle when you open the basket, and visually aim for edges turning glossy and golden to deep brown. Shake the basket gently every few minutes so hot air hits all sides evenly. A common slip is not checking early enough and ending up with overcooked, shriveled mushrooms.
Transfer to a plate and immediately season with a pinch of salt: Right after cooking, the mushrooms will be at their juiciest and most aromatic, so a final pinch of kosher salt heightens the flavors. The residual heat helps the salt dissolve and distribute evenly. If you salt too early, the mushrooms can become waterlogged as salt draws out moisture during marination and cooking.
Sprinkle with herbs if desired: At this finishing moment add finely chopped parsley or rosemary so the fresh oils and scents stay vivid against the warm mushrooms. The herb's bright green or piney scent will pop when contrasted with the cooked, savory fungi. Don’t add herbs before cooking, as their delicate notes can be lost or singed by the high heat.